The invention is directed to metallodielectric photonic crystals (MDPCs) which exhibit both unidirectional and omnidirectional photonic band gaps.
Photonic crystals are of great interest in the field of electromagnetics because certain types of photonic crystals exhibit a photonic band gap or stop band. The band gap defines a range of frequencies at which electromagnetic radiation striking the crystal is reflected by the crystal rather than being permitted to propagate through it.
The typical photonic crystal is a spatially periodic structure. One well-known photonic crystal is formed of multiple elements of a dielectric material arranged in a three-dimensional lattice. Other crystals exhibit two-dimensional periodicity in which elongated, e.g. cylindrical, elements made of dielectric material are arranged in a two-dimensional periodic pattern with their longitudinal axes parallel to each other.
In these crystals, the dimensions of the lattice structures and the dielectric elements are selected to produce band gaps having desired center frequencies and bandwidths. Electromagnetic radiation at a frequency within the band gap is reflected from the structure via the well-known Bragg reflection phenomenon.
As previously described, three-dimensionally periodic structures can give rise to photonic band gaps, characterized by the absence of propagation of electromagnetic radiation along directions in space. To date, the structures studied have consisted of a combination of two or more lossless dielectric materials. In general, the size of the band gaps in these conventional all-dielectric crystals is less than 30% of the center frequency and the maximum rejection is less than 10 dB per lattice constant. The limited rejection follows partly from the finite size of the band gaps. By increasing the size of the gap, the rejection coefficient can be significantly increased.
It is therefore an object of the present invention to provide an improved photonic crystal which exhibits an increased band gap size with respect to conventional crystals.
It is another object of the invention to provide a metallodielectric photonic crystal which not only gives rise to large rejection along certain directions in space, but along every direction.